The present invention relates to a control apparatus of an internal combustion engine which is capable of suppressing undesirable torque variation not intended by a driver.
Furthermore, this invention relates to a cylinder injection type internal combustion engine which selectively changes the combustion mode in accordance with engine operating conditions between a stratified combustion mode (i.e., combustion mode injecting fuel at a compression stroke) and a homogeneous combustion mode (i.e., combustion mode injecting fuel at an intake stroke).
Moreover, this invention relates to a control apparatus of an internal combustion engine which controls the engine based on an intended torque request.
Recent trend of low fuel consumption, low exhaust emission, and high output power is increasing the necessity of cylinder injection type internal combustion engine (i.e., direct injection engine). The unexamined Japanese patent publication 10-47111 discloses a cylinder injection engine. When the engine operates in a low load condition, a small amount of fuel is directly injected into a cylinder at a compression stroke to form a stratified mixture in the cylinder for realizing stratified combustion which is advantageous to improve fuel economy. On the other hand, in a high load condition, a relatively large amount of fuel is directly injected into a cylinder at an intake stroke to form a uniform or homogeneous mixture in the cylinder for realizing uniform or homogeneous combustion which is advantageous to produce high output power.
According to the cylinder injection engine, it is necessary to maintain stable combustion condition before and after switching of combustion mode. To this end, generally performed is adjustment of a throttle opening degree and/or adjustment of an exhaust gas recirculation (i.e., EGR) amount. However, changing the throttle opening degree and/or the EGR valve opening degree induces a change of air-fuel ratio in the cylinder as well as a change of pumping loss. This possibly causes undesirable variation or fluctuation of an axle torque of the engine, causing a significant torque shock.
The unexamined Japanese patent publication 11-22517 introduces a control system correcting the air-fuel ratio in response to the switching from the stratified combustion mode (i.e., combustion mode injecting fuel at a compression stroke) to the homogeneous combustion mode (i.e., combustion mode injecting fuel at an intake stroke) or vice versa.
However, adjusting the air-fuel ratio in response to the switching of combustion mode will cause undesirable shift of the air-fuel ratio which possibly brings the combustion of engine into an unstable condition.
Regarding the undesirable torque variation or shock caused by the switching of combustion mode, similar problems will occur in lean burn engines which change the air-fuel ratio between a lean operation and a stoichiometric/rich operation.
Furthermore, according to recent electronically controlled engines, realizing good drivability responsive to a driver""s accelerator operation is very important. For example, an driver""s requested acceleration force (torque) can be estimated based on a throttle opening degree, a fuel injection amount, and an ignition timing etc. This is generally referred to as torque on demand control (refer to unexamined Japanese patent publication 11-50889).
However, if the intended torque request is calculated based on only a static torque loss (such as mechanical friction loss and pumping torque loss), the response of the vehicle does not meet the driver""s request in an accelerating condition where the engine speed promptly changes in a wide range.
In view of the problems of the conventional engine control techniques, the present invention has an object to provide a control apparatus for an internal combustion engine which is capable of suppressing undesirable torque variation while maintaining stable combustion even in a situation where control parameters inducing a significant torque variation are adjusted.
To accomplish the above and other related objects, the present invention provides a first control apparatus for an internal combustion engine comprising judging means for judging a torque amount requested by a driver, and control means for controlling operating conditions of an internal combustion engine based on the requested torque amount. Furthermore, the first control apparatus includes torque variation suppressing means, responsive to adjustment of a subjective control parameter causing a significant torque variation according to the engine operating conditions, for converting a torque variation amount to be caused by the adjustment of the subjective control parameter into an equivalent adjustment amount of a supplementary control parameter non-relevant to the adjustment of the subjective control parameter, and for changing the supplementary control parameter by the equivalent adjustment amount so as to suppress the torque variation amount to be caused.
For example, when a throttle opening degree and an exhaust gas recirculation (EGR) amount are changed to maintain stable combustion condition, the torque variation to be caused by these control parameters is converted into an equivalent adjustment amount of other control parameters, such as fuel amount, ignition timing, etc, which are non-relevant to the adjustment having done by the above control parameters. Then, the non-relevant control parameters are changed so as to cancel the torque variation to be caused by the adjustment having done by the above control parameters. Thus, it becomes possible to suppress undesirable torque variation while maintaining combustion stability. This brings improved drivability of the vehicle.
The first control apparatus can be applied to each of a lean burn engine, an intake port injection engine, and a cylinder injection engine.
When the first control apparatus is employed in the cylinder injection engine, it is preferable that the first control apparatus further comprises combustion mode switching means for selecting either a stratified combustion mode or a homogeneous combustion mode in accordance with the engine operating conditions, so that fuel is directly injected into a cylinder at a compression stroke to cause stratified combustion when the stratified combustion mode is selected and at an intake stroke to cause homogeneous combustion when the homogeneous combustion mode is selected. In this case, the torque variation suppressing means suppresses torque variation responsive to a change of a control parameter adjusted to maintain stable combustion condition before and after switching of the combustion mode by correcting a fuel amount when the stratified combustion mode is selected and by correcting an air amount and/or an ignition timing when the homogeneous combustion mode is selected.
It is further preferable that the torque variation suppressing means of the first control apparatus corrects the requested torque amount when the requested torque amount is converted into the fuel amount in the stratified combustion mode and corrects the requested torque amount when the requested torque amount is converted into the air amount in the homogeneous combustion mode.
Furthermore, the present invention provides a second control apparatus for a cylinder injection type internal combustion engine comprising combustion mode switching means for selecting either a stratified combustion mode or a homogeneous combustion mode in accordance with engine operating conditions, so that fuel is directly injected into a cylinder at a compression stroke to cause stratified combustion when the stratified combustion mode is selected and at an intake stroke to cause homogeneous combustion when the homogeneous combustion mode is selected. The second control apparatus comprises stratified combustion mode controlling means for obtaining a target fuel amount based on an indicated torque request to be generated from the internal combustion engine during the stratified combustion mode as well as based on an engine rotational speed, and for obtaining other control parameter by using the target fuel amount. The second control apparatus further comprises homogeneous combustion mode controlling means for obtaining a target air amount based on an indicated torque request to be generated from the internal combustion engine during the homogeneous combustion mode as well as based on the engine rotational speed, and for obtaining other control parameter by using the target air amount.
According to the second control apparatus, it is preferable that indicated torque request calculating means is provided for calculating the indicated torque request, and each of the stratified combustion mode controlling means and the homogeneous combustion mode controlling means uses the indicated torque request obtained by the indicated torque request calculating means.
Furthermore, according to the second control apparatus, it is preferable that target air-fuel ratio setting means is provided for setting a target air-fuel ratio based on the indicated torque request and the engine rotational speed. The stratified combustion mode controlling means calculates a target air amount and a target throttle opening degree based on the target air-fuel ratio determined by the target air-fuel ratio setting means as well as based on the target fuel amount. And, the homogeneous combustion mode controlling means calculates a target fuel amount based on the target air-fuel ratio determined by the target air-fuel ratio setting means as well as based on a detection value or an estimated value of an actual air amount.
Moreover, in view of the problems of the conventional engine control techniques, the present invention has an object to provide a control apparatus for an internal combustion engine which is capable of performing an excellent torque on demand control assuring good engine response in a vehicle accelerating condition.
To accomplish the above and other related objects, the present invention provides a third control apparatus for an internal combustion engine comprising indicated torque request calculating means for calculating an indicated torque request to be generated from the internal combustion engine for controlling the internal combustion engine based on the indicated torque request. The indicated torque request calculating means calculates the indicated torque request considering a dynamic torque loss caused by an inertial force responsive to a change of engine rotational speed in addition to a static torque loss of the internal combustion engine.
According to the third control apparatus, it is preferable that the indicated torque request calculating means calculates the dynamic torque loss by multiplying an inertial moment of a rotary member rotating in synchronism with a crankshaft of the internal combustion engine with a rotational angular acceleration.
Furthermore, according to the third control apparatus, it is preferable that the indicated torque request calculating means obtains the indicated torque request by adding a requested axle torque, the dynamic torque loss, the static torque loss, and an external load torque of an accessory or the like installed on the internal combustion engine.